U.S. patent application number 11/940775 was filed with the patent office on 2010-01-28 for apparatus and method for near-field communication.
This patent application is currently assigned to Integration Associates Inc.. Invention is credited to Robert Farmer, Wayne T. Holcombe, Pavel Konecny, Jean-Luc Nauleau, Miroslav Svajda.
Application Number | 20100021176 11/940775 |
Document ID | / |
Family ID | 41568759 |
Filed Date | 2010-01-28 |
United States Patent
Application |
20100021176 |
Kind Code |
A1 |
Holcombe; Wayne T. ; et
al. |
January 28, 2010 |
Apparatus and Method for Near-Field Communication
Abstract
A communication device is disclosed having optical and
near-field communication capability. The device includes an optical
transceiver circuit fabricated on an integrated circuit die and
configured to transmit and receive far field signals. A near field
transceiver circuit is also fabricated on the integrated circuit
die and is configured to transmit and receive near-field
electro-magnetic signals. Control circuitry is provided to
selectively enable the optical transceiver circuit and the near
field transceiver circuit responsive to an external control
signal.
Inventors: |
Holcombe; Wayne T.;
(Mountain View, CA) ; Konecny; Pavel; (Sunnyvale,
CA) ; Svajda; Miroslav; (Sunnyvale, CA) ;
Nauleau; Jean-Luc; (Los Gatos, CA) ; Farmer;
Robert; (Modesto, CA) |
Correspondence
Address: |
FRANCISSEN PATENT LAW, P.C.
65 W. JACKSON BLVD, SUITE # 138
CHICAGO
IL
60604
US
|
Assignee: |
Integration Associates Inc.
Mountain View
CA
|
Family ID: |
41568759 |
Appl. No.: |
11/940775 |
Filed: |
November 15, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60859378 |
Nov 16, 2006 |
|
|
|
Current U.S.
Class: |
398/115 ;
455/41.1 |
Current CPC
Class: |
H04B 10/1143 20130101;
H04B 5/02 20130101 |
Class at
Publication: |
398/115 ;
455/41.1 |
International
Class: |
H04B 10/00 20060101
H04B010/00; H04B 5/00 20060101 H04B005/00 |
Claims
1. A communication device having optical and near-field
communication capability, the device comprising: an integrated
circuit die; an optical transceiver circuit fabricated on the
integrated circuit die and configured to transmit and receive
optical signals; a near field transceiver circuit fabricated on the
integrated circuit die and configured to transmit and receive
near-field electro-magnetic signals; and control circuitry
configured to selectively enable the optical transceiver circuit
and the near field transceiver circuit responsive to an external
control signal.
2. The communication device of claim 1, the device further
comprising an external shield, and where the integrated circuit die
includes an antenna interface pin electrically coupled to the
external shield, where the near field transceiver circuit is
electrically coupled to the antenna interface pin for receiving
near field signals using the external shield.
3. The communication device of claim 2, where the integrated
circuit die includes a transmit data interface pin electrically
coupled to the external shield where a baseband data signal applied
to the transmit data interface pin also drives the external shield
to transmit near field signals using the external shield.
4. The communication device of claim 2, the device further
comprising a transmit antenna, and where the integrated circuit die
includes a transmit antenna interface pin electrically coupled to
the transmit antenna, where the near field transceiver circuit is
electrically coupled to the transmit antenna interface pin for
transmitting near field signals using the transmit antenna.
5. The communication device of claim 2, the device further
comprising a transmit antenna, and where the integrated circuit die
includes a transmit data interface pin electrically coupled to the
transmit antenna, where a baseband data signal applied to the
transmit data interface pin also drives the transmit antenna.
6. The communication device of claim 2, wherein a pairing
controller is coupled to the far field transceiver circuit, where
the pairing controller is configured to send and receive pairing
control messages using the near field transceiver circuit in order
to establish a far field communication link with another device
having another near field transceiver circuit and another pairing
controller.
7. The communication device of claim 1, where the optical
transceiver circuit further comprises an IrDA specification
compliant transceiver.
8. The communication device of claim 1, where the near field
transceiver circuit is further configured to sense a resistance
coupled to an interface pin of the integrated circuit die and set
an operating parameter of the near field transceiver circuit based
on a magnitude of the sensed resistance.
9. A method for providing near field communication capability in a
transceiver device, the method comprising the steps of: fabricating
an optical transceiver circuit and a near field transceiver circuit
on an integrated circuit die, where the optical transceiver circuit
is configured to transmit and receive optical signals, and further
wherein the near field transceiver circuit is configured to
transmit and receive near-field electro-magnetic signals; and
providing control circuitry for selectively enabling the optical
transceiver circuit and the near field transceiver circuit
responsive to a control signal.
10. The method of claim 9, the method further comprising the steps
of providing an external shield for shielding the integrated
circuit die from noise; electrically coupling the external shield
to the integrated circuit die; and receiving near field signals
using the external shield.
11. The method of claim 10, the method further comprising the steps
of: electrically coupling a transmit antenna to the integrated
circuit die; and transmitting near field signals using the transmit
antenna.
12. The method of claim 10, the method further comprising the steps
of: electrically coupling a transmit antenna to the integrated
circuit die; and near field transmitting a baseband data signal by
directly applying the baseband data signal to the transmit
antenna.
13. The method of claim 10, the method further comprising the step
of near field transmitting a baseband data signal by directly
applying the baseband data signal to the external shield.
14. The method of claim 10, the method further comprising the steps
of: providing pairing control for sending and receiving pairing
control messages using the near field transceiver circuit; and
establishing a far field communication link with another device
having another near field transceiver circuit and another pairing
controller by exchanging pairing control messages with the another
device.
15. The method of claim 9, the method further comprising the steps
of: sensing a resistance present at an interface of the integrated
circuit die; and setting an operating parameter of the near field
transceiver circuit based on a magnitude of the sensed
resistance.
16. An integrated circuit device, the device comprising: long range
communication means for performing at least one of transmitting and
receiving long range signals; near field communication means for
performing at least one of transmitting and receiving near-field
electro-magnetic signals; control means for selectively enabling
the long range and near field communication means responsive to a
control signal.
17. The device of claim 16, the device further including external
shielding means for shielding the integrated circuit device from
noise, the external shielding means being electrically coupled to
the integrated circuit device for receiving near field signals.
18. The device of claim 17, the device further including transmit
antenna means electrically coupled to the integrated circuit device
for transmitting near field signals.
19. The device of claim 17, the device further including transmit
antenna means electrically coupled to the integrated circuit device
for near field transmitting a baseband data signal by directly
applying the baseband data signal to the transmit antenna
means.
20. The device of claim 17, the device further including pairing
control means for sending and receiving pairing control messages
using the near field communication means in order to establish a
long range communication link with another device using the long
range communication means.
21. The system for near field communication, the system comprising:
a first integrated circuit device, the first device having formed
thereon a first transceiver circuit, a near field transceiver
circuit, and control circuitry for selectively enabling one of the
first transceiver circuit and the near field transceiver circuit
responsive to an external control signal; and a second integrated
circuit device, the second device having formed thereon a near
field transceiver circuit, where the near field transceiver of the
first device and the near field transceiver of the second device
are capacitively coupled to one another in order to exchange near
field data signals.
22. The system of claim 21, wherein: the first integrated circuit
device further includes a pairing controller configured to send
messages using the near field transceiver of the first device; and
the second integrated circuit device further includes a first
transceiver circuit and a pairing controller configured to receive
messages using the near field transceiver of the second device, the
pairing controller of the second device being configured to receive
messages from the pairing controller of the first integrated
circuit device in order to establish a communication link between
the first transceiver of the first integrated circuit device and
the first transceiver of the second integrated circuit device.
23. The system of claim 22, where the near field transceivers of
the first and second integrated circuit devices are each configured
to communicate with one another in a half duplex manner.
24. The system of claim 22, where the first transceiver of the
first integrated circuit device and the first transceiver of the
second integrated circuit device each further comprise an optical
transceiver.
25. The system of claim 22, where the first transceiver of the
first integrated circuit device and the first transceiver of the
second integrated circuit device each further comprise a radio
frequency transceiver.
26. The system of claim 21, where the near field transceiver of the
first integrated circuit device is further configured to transmit a
baseband data signal.
27. The system of claim 21, where the first transceiver circuit of
each of the first and second integrated circuit devices further
comprises a USB transceiver.
28. The system of claim 27, where the near field transceiver
circuits of each of the first and second integrated circuit devices
are further configured to provide a secondary communication channel
for the USB transceivers of the first and second integrated circuit
devices.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This patent application claims the benefit of U.S.
Provisional Patent Application No. 60/859,378 filed Nov. 16, 2006
and hereby incorporates this application by reference in its
entirety.
FIELD OF THE INVENTION
[0002] This invention pertains to data communication and, more
particularly, short range communication.
BACKGROUND OF THE INVENTION
[0003] Infrared data communication is a known technique for short
range data communications. The Infrared Data Association (IrDA)
defines protocols for one example of an infrared communications
scheme. An IrDA infrared communication transceiver typically
provides 115.2 Kbp to 16 Mbs wireless transfer of data transfer
over less than one meter. It uses a "point and beam" paradigm to
transfer variable length data files; such as, speed directory lists
on cell phones or PDA, MP3 files, pictures, or video clips.
Although it is a wireless or cable replacement technology, IrDA is
not suitable for networking like RF (Radio Frequency) IEEE 802.11
Wi-Fi or Bluetooth radio frequency protocols since it does not have
sufficient range and only works within the +/-15 degree "point and
beam" cone.
[0004] The following references provide additional background for
the present invention. U.S. Pat. No. 4,763,340 for capacitive
coupling type data transmission circuit for portable electronic
apparatus. U.S. Pat. No. 3,265,972 for underwater electrical field
communication system. U.S. Pat. No. 4,292,595 for capacitance
coupled isolation amplifier and method. U.S. Pat. No. 6,141,592 for
data transmission using a varying electric field. U.S. Pat. No.
6,336,031 for wireless data transmission over quasi-static electric
potential fields. U.S. Pat. No. 5,621,913 system with chip to chip
communication. U.S. Pat. No. 6,751,691 arrangement for data
transfer between a computer and peripheral device or other data
processing device. U.S. Pat. No. 6,612,852 for contactless
interconnection system. U.S. Pat. No. 4,918,737 for hearing aid
with wireless remote control. U.S. Pat. No. 5,437,057 for Wireless
communications using near-field coupling. U.S. Pat. No. 4,061,972
for Short range induction field communication system. U.S. Pat.
Nos. 5,864,591 and 6,240,283 for Feedback mitigation. Fazzi, A. et
al; "A 0.14 mW/Gbps High-Density Capacitive Interface for 3D System
Integration," Proceedings of CICC 2005 Conference, San Jose, pp.
101-104. Drost, R. et al. "Proximity communication," IEEE J.
Solid-State Circuits, Volume 39, Issue 9, pp. 1529-1535, September
2004.
[0005] The following websites provide additional information
regarding communications systems:
[0006]
http://www.reghardware.co.uk/2006/04/19/nokia_cashless_bus_tickets/
[0007] http://www.nokia.com/nfc
[0008] http://www.theregister.co.uk/2004/07/22/aura_wireless/
[0009] http://www.auracomm.com/site/content/llla116.asp
[0010] http://www.sony.net/Products/felica/abt/dvs.html
[0011]
http://www.research.ibm.com/journal/sj/353/sectione/zimmerman.html
[0012]
http://www.evaluationengineering.com/archive/articles/1005/1005the_-
world.asp
[0013]
http://www.eetasia.com/ART.sub.--8800412880.sub.--590626_a6f100b720-
0604.HTM
BRIEF SUMMARY OF THE INVENTION
[0014] In one embodiment, a communication device is provided having
optical and near-field communication capability. The device
includes an optical transceiver circuit fabricated on an integrated
circuit die and configured to transmit and receive optical signals.
A near field transceiver circuit is also fabricated on the
integrated circuit die and is configured to transmit and receive
near-field electro-magnetic signals. Control circuitry is provided
to selectively enable the optical transceiver circuit and the near
field transceiver circuit responsive to an external control
signal.
[0015] In an embodiment of a method for providing near field
communication capability in an optical transceiver device, the
method calls for fabricating an optical transceiver circuit and a
near field transceiver circuit on an integrated circuit die, where
the optical transceiver circuit is configured to transmit and
receive optical signals, and further wherein the near field
transceiver circuit is configured to transmit and receive
near-field electro-magnetic signals. The method also calls for
providing control circuitry for selectively enabling the optical
transceiver circuit and the near field transceiver circuit
responsive to a control signal.
[0016] In an embodiment of a system for near field communication,
the system includes a first integrated circuit device that includes
a first transceiver circuit, a near field transceiver circuit, and
control circuitry that selects one of the first transceiver circuit
and the near field transceiver circuit for operation responsive to
an external control signal. The system also includes a second
integrated circuit device that includes a near field transceiver
circuit. The near field transceiver of the first device and the
near field transceiver of the second device are capacitively
coupled to one another in order to exchange near field data
signals.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Certain exemplary embodiments are described below with
respect to the following figures, wherein:
[0018] FIG. 1 is a cross-sectional diagram illustrating a
communication link having two devices, where each device includes
an infrared transceiver and a near-field transceiver that utilizes
a capacitive near-field antenna;
[0019] FIG. 2 is a cross-sectional diagram illustrating a
communication link having two devices, where each device includes
an infrared transceiver and one device uses an inductive near-field
transceiver that utilizes a auxiliary inductive loop transmit
antenna (TX) for transmitting a baseband data signal, while the
other device utilizes an external shield as a capacitive antenna to
transmit a baseband data signal;
[0020] FIG. 3 is a cross-sectional diagram illustrating a
communication link having two devices, where each device includes
an infrared transceiver and a near-field transceiver that utilizes
a capacitive near-field antenna as well as an auxiliary capacitive
transmit antenna and adjustment resistors;
[0021] FIG. 4 is a circuit diagram illustrating an example of a
transmitter and receiver pair showing capacitive near-field
coupling;
[0022] FIG. 5 is a circuit diagram illustrating an example of a
transmitter and receiver pair illustrating inductive near-field
coupling;
[0023] FIG. 6 is a diagram illustrating an example of a near-field
communication link between a cell phone device with near-field
enabled IRDA transceiver and a Bluetooth headphone device with
near-field transceiver for use in pairing control;
[0024] FIG. 7 is a diagram illustrating an example of a near-field
communication link between a cell phone device and a hearing aid
device;
[0025] FIG. 8 is a transistor diagram illustrating an exemplary
embodiment of a receiver circuit for use with a capacitive
near-field transceiver device;
[0026] FIG. 9 is a transistor diagram illustrating one exemplary
embodiment of a comparator circuit in the circuit of FIG. 8;
[0027] FIG. 10 is a transistor diagram illustrating one exemplary
embodiment of a multiplexor circuit in the circuit of FIG. 8;
[0028] FIG. 11 is a transistor diagram illustrating one exemplary
embodiment of a bias current generating circuit in the circuit of
FIG. 8;
[0029] FIG. 12 is a functional block diagram illustrating an
embodiment of a transceiver configured to operate in infrared and
near-field modes;
[0030] FIG. 13 is a functional block diagram illustrating an
example of the transceiver of FIG. 12 operating with a controller
the switches the transceiver between infrared and near-field modes
and interfaces with a microprocessor;
[0031] FIG. 14 is a circuit diagram illustrating an example of a
capacitive receiver for use in receiving signals in a capacitive
near-field transceiver device;
[0032] FIG. 15 is a functional block diagram illustrating an
example of devices utilizing a USB transceiver and a near field
transceiver, where the near field transceiver may provide an easily
accessible data port or a secondary channel for a USB link; and
[0033] FIG. 16 is a functional block diagram illustrating an
example of devices utilizing an infrared USB transceiver and a near
field transceiver, where the near field transceiver may provide an
easily accessible data port or a secondary channel for a USB
link.
DETAILED DESCRIPTION OF THE INVENTION
[0034] While some of the characteristics of an IrDA infrared
communication transceiver may be viewed as limitations, these same
characteristics can be advantageous, such as by providing
eavesdropping security, implicit addressability, and ease of use
over RF solutions. Also, IrDA transceivers typically have less than
one tenth the cost, size, and idle receiver current consumption of
comparable data rate radio frequency physical layer data
transceivers.
[0035] At present, IrDA transceivers have approximately 30%
penetration in Asian and European cell phone markets and nearly
100% of the PDA (Personal Digital Assistants) market. In year 2006,
the total market for IrDA transceivers exceeds 250 million
units.
[0036] Presently, there is significant market interest in using
IrDA transceivers for increasingly larger file transfers. Due to
the advent of small, low cost, high density memory both flash and
small hard disk drives that allow over 1 gigabyte of data storage
in small handheld devices; such as, cell phones, MP3 audio and
video players, digital cameras, etc., there is strong interest in
some form of low cost, connector-less, high-speed file transfer
communication system. As of this date, very small, low cost 4 Mbps
Fast Infrared (FIR) IrDA transceivers are available that have costs
similar to 115 Kbps devices. These devices have ranges close to 1
meter. Higher cost and in larger packages, 16 Mbps Very Fast
Infrared (VFIR) transceivers are available, and development of
small module 16 Mbs devices are on going.
[0037] In addition, there is interest in Ultra-Fast Infrared (UFIR)
devices that have transfer rates of around 100 Mbps. These higher
rates would be desirable to allow downloading of large files from,
for example, pay-for-use kiosks or from a user's library in a
convenient amount of time. A typical MP3 song requires about one
Megabyte or eight Megabits of memory per minute of play time while
a TV quality compressed video takes about 1.2 Gigabyte or 9.6
Gigabits per hour of play time. At 16 Mbps, a 4 minute MP3 song
would take 2 seconds to down load while a 2 hour video would take
20 minutes to down load. At slower 4 Mbps, these down load times
increase by a factor of four. For MP3 songs, pictures and short
video clips, the 4 Mbps and 16 Mbps transfer rates are reasonable
fast for transfer-and-go applications but for transferring program
videos, it is excessively slow. For full feature video down loads,
a 100 Mbps would be more desirable, requiring a bit over 3 minutes
for down load. Even better yet, data rate speeds of greater than
480 Mbps comparable to USBII would allow transferring a 2 hour
video in about 40 seconds.
[0038] However, development of a low cost 100 Mbps IrDA transceiver
may be many years off, let alone a 480 Mbps system. As the data
rate goes up, the bandwidth and sensitivity goes down requiring
higher transmit irradiance levels. A key issue is that 1 meter or
even 20-30 cm range will never be possible at 100 Mbps with the
standard IrDA 100 mW/Sr (Sr>Steradian) optical transmit level.
Even at 16 Mbps in a small module, 1 meter range is probably not
practically possible. Higher optical transmitter levels would
require expensive solid state laser technology and eye safety
issues would limit irradiance to a maximum of about 500 mW/Sr in
small modules.
[0039] Consequently, at 100 Mbps, the practical transfer distance
with a 100 Mw/SR optical transmitter would fall to only a few
centimeters. At these distances, the IrDA point and beam paradigm
becomes problematic due to optical alignment requirements of both
receiver and transmitter. It would be better to use some form of
proximity data transfer technique less critical of alignment and
that has fewer technical hurdles to high speed data transfer.
[0040] Another issue becoming more of a concern for all wireless
data transfer is security against unauthorized eavesdropping.
Standard RF wireless systems have ranges of 100+ meters and are
vulnerable. Short range IrDA already provides reasonable security
by virtue of its 20-30 cm range. However, for financial
transactions, which are typically fairly low data rate
applications, even shorter distances in the 1-10 cm range may be
more secure. For pay-per-use applications both very high speed data
transfer and immunity against unauthorized eavesdropping is
desirable.
[0041] Long range wireless systems also have implicit
addressability or pairing issues due to numerous other devices
within range. For example, a Bluetooth headset normally only needs
to connect to a single device such as a cell phone, but there maybe
dozens or even hundreds of users within Bluetooth range. Although
Bluetooth and similar wireless protocols can co-exist with hundreds
of users, pairing is critical; that is, both ends of the connection
pair need to identify each other. Typically this requires each to
device to acquire addresses and configuration parameters; such as,
frequency, data rate, modulation, encryption, etc. Although the
cell phone typically has a keyboard and display, making pairing
data entry possible, it is still an inconvenient to enter this
data. For a headphone without display or keyboard entering anything
but very simple parameters is a severe obstacle to use. More
typically, headphone and cell phone pairing use some synchronizing
method or system to indicate that these two devices need to talk to
each other.
[0042] One method for pairing is for the user to push a
synchronizing button on each device at the same time. Each device
looks via the wireless link for another device that is also has its
synchronizing button pushed and assumes this is device it should
pair with. Or, in the headphone/cell phone Bluetooth synchronizing
example, the head phone is held close to the cell phone when a
button on one device is pushed, it synchronizes to the device that
has the largest signal that is presumably the closest. The latter
requires RSSI (Receive Signal Strength Indicator) that may not
reliably determine the range from the signal strength since the
main purpose of RSSI is not ranging but determination whether a
channel is occupied or available for communication. In addition,
other Bluetooth devices may still be able to listen to the
synchronizing process to facilitate eavesdropping. Even with
encryption, devices need to pass starting keys back and forth, but
if these are eaves dropped, security is compromised unless using
large prime number based public key encryption systems. However,
these public key systems are not always practical for these type of
applications requiring extensive signal processing and access to a
data base of large prime numbers, neither of these may be available
in a battery powered headphone.
[0043] Transfer of configuration parameters is another application
similar to file transfer. Unlike large file transfers, high speed
is not necessary or desirable. An example is a modern digital
hearing aid. These devices generally require an upload of various
digital filter and gain coefficients; i.e., adjustments for each
individual's hearing response. Typically, like financial
transactions no more than several hundred bits of information needs
to be transferred at very short range. Generally, it is desirable
that some form of contact-less serial communication be used since a
wire contact connection is problematic due to normal earwax
accumulations and a connector is too large. Although a very small
low speed IrDA transceiver module would work, it is not smaller
than a mechanical contact and is larger than desired for a hearing
aid. IrDA transceiver also requires an unobstructed optical window,
which is undesirable from aesthetical reasons (a uniform, skin-like
appearance of hearing aid is preferred).
[0044] Similar to passing parameters, in the same hearing aid
example, it would be desirable to have a unidirectional or
bidirectional low speed short range communication path between the
hearing aid and cell phone that allows the cell phone to directly
pass digitized headphone audio directly to the hearing aid digital
signal processor. This allows the hearing aid to mute background
acoustical noise while telephone speech is being received, in
addition to audio shaping of the telephone audio for the hearing
deficits. Again an IrDA transceiver could be used for this
application except it is too large but also the IrDA transceiver is
not normally placed on the cell phone in a way to beam into the
ear.
[0045] A more convenient solution proposed for wireless pairing has
been the use a capacitive touch or proximity modulated carrier
based near field system to provide pairing communication. Although
this concept is viable, its cost is similar to that of any radio
system. Argue-ably, 115.2 Kbps IrDA transceivers can provide this
function at lower cost than a modulated carrier based near field
system. Currently, these systems require only 1.2 sqmm of silicon
plus a 1 sqmm photodiode and an infrared LED in a simple plastic
lensed module. Total semiconductor costs are less than $0.15.
Although, the near-field modulated carrier systems proposed for
this function have data rates of 100 Kbps to 424 Kbps, this is not
a compelling speed for proximity file transfer since it does not
approach the speeds of existing Wi-Fi wireless, USBII, or even high
speed IrDA.
[0046] Similar to the above example, various near-field
technologies have been used or proposed for decades to perform low
to medium speed communication in a limited proximity, often
unidirectionally. Near-field is typically understood to mean the
region within one wavelength of an antenna, where the electric and
magnetic fields are not related to each other solely by the
characteristic impedance of free space. Near-fields are the larger
non-propagating fields of an antenna. Conventional radio
communication arises from the propagating far-fields although it
will work in the near-fields.
[0047] Antennas much smaller than a half wavelength radiate very
poorly at far-field or long ranges even though they have very large
near-fields. The far-field power radiation efficiency of these
antennas is proportional to the inverse of the fourth power of
their driving frequency voltage or current. Despite their poor
far-field radiation resistance in the near-field, these short
near-field antennas can also have very wide bandwidth, much wider
than a half wave dipole in the far-field. Both of these
characteristics make it possible to have wideband communication at
short distances with good signal to noise while keeping far-field
radiation below regulatory radiated limits for general electronic
devices. Consequently, most near-field communication systems use
antennas that are much smaller than the wavelength. U.S. Pat. No.
5,437,057 provides a description of inductive near-field
transmission.
[0048] One advantage of a near-field system is that it can transfer
significant power over a very short variable distance, e.g. less
than 1 centimeter, without excessive long range or far field
radiation, e.g. on the order of 10 centimeters or farther. As a
consequence, near-fields have been used to provide power for RF ID
applications. Inductive carrier systems are typically used because
low frequency (less than 10 MHz) power transfer is more easily and
efficiently coupled with a high Q ferrite loop antenna tuned for
resonance. Although capacitive carriers could be used, at
frequencies under 100 MHz, it is difficult to transfer sufficient
power through the at most several pico farads of coupling
capacitance.
[0049] For capacitive near field, the transmit antenna is a
sub-half-wave plate or wire driven with a voltage source and the
resulting electrostatic near field is directly proportional to the
antenna voltage. For inductive near field, the transmit antenna is
a sub-half-wave loop driven with a current source, and the
inductive near field is directly proportional to the loop current.
For both, the field level is relatively independent of frequency as
long as it is well below the antenna's characteristic
frequency.
[0050] In this frequency range the largest part of the near-field
electrostatic field coupling can be modeled as a small capacitor
and the magnetic field coupling can be modeled as an inefficient
transformer. Radiating fields will be a smaller contributor to
coupling. FIG. 4 is a circuit diagram illustrating an example of a
transmitter and receiver pair modeling capacitive near-field
coupling. FIG. 5 is a circuit diagram illustrating an example of a
transmitter and receiver pair modeling inductive near-field
coupling.
[0051] In FIG. 4, a transmitter 300 includes a transmit driver 302
that drives antenna 306 that is also capacitively coupled to ground
through capacitor 304. Transmit antenna 306 is near-field coupled
to receive antenna 322 of receiver 320, where the resulting
capacitive coupling is represented by capacitor 308. In this
example, the transmitted baseband signal is received as a series of
spikes that are input to transconductance amplifier 330, which
compares the received signal to a REFERENCE voltage signal provided
by voltage reference 336. The output of transconductance amplifier
330 is input to operation amplifier 340, which produces a received
data signal.
[0052] In FIG. 5, transmitter 350 includes driver 352 that uses a
transmit signal to drive an inductor 356 that is near field
inductively coupled to inductor 362 of receiver 360. The
transmitted baseband signal is received as a series of spikes that
are input to transconductance amplifier 370, which compares the
received signal to a REFERENCE voltage signal provided by voltage
reference 376. The output of transconductance amplifier 370 is
input to operation amplifier 380, which produces a received data
signal.
[0053] Standard electronic components capacitors, inductors and
transformers can be thought of as extreme near-field devices. For
these devices the near-fields are used to transfer or store energy
with over 90% efficiency. For near-field signal communication,
efficiency of signal transfer may be much less than 1%. In fact, if
the transfer efficiency is improved by making the antenna resonant,
the far-field radiating efficiency also increases.
[0054] Commonly a near-field antenna will radiate mostly one type
of near-field. A short wire or plane antenna relative to a dipole
will have mostly electrostatic fields within its near-field and
very little magnetic field while a small loop antenna relative to a
dipole will have mostly magnetic fields and very little
electrostatic fields within its near-field. Unlike far-field radio
waves where any aspect of the environment that shields either the E
field or H field will significantly attenuate the other field, with
near-field this is not true. There is much less interaction between
the two fields. This can be used to advantage depending on both the
shielding and noise characteristics of the environment.
[0055] For example, induction loop systems have been used to send
communication to induction pickup devices within the loop. The loop
may be run around the room or area to allow communication within
the area. Electronic dog fences are inductive systems that use a
receiver on the dog collar to sense a signal in a buried wire via
its magnetic component. When the dog gets within a few feet of the
buried wire the received signal triggers a shock. The electrostatic
component of the buried wire would be shielded by the ground
conductivity but the magnetic component is much less affected
especially at low frequencies much below the half wavelength size
of the loop. The electronic dog fence takes advantage that the
inductive near-field signal falls off rapidly only a few feet from
the radiating wire.
[0056] As a result, one aspect of hand-held near-field systems is
that they can provide large immunity to external electro magnetic
interference by moving the proximity of the antennas as close as
necessary to achieve good signal to noise. Small decreases in range
will cause large increases in signal level. Generally, once the
proximity needs to be less than a few centimeters, users do not
differentiate differences in range necessary to make communication
occur, especially on small handheld devices. Users can be guided
with signal strength displays to encourage them to place devices
within close enough range for good signal quality. Because of their
larger signals and operation outside regulated frequency limits,
and because they do not radiate, near-field transceivers are
simpler than far-field systems without need for expensive RF
components.
[0057] The signal level of both a capacitive and inductive
near-field signal decreases very rapidly with distance. How it
changes is a function of the size and shape of the transmitting and
receiving antennas, distance and amount of local shielding. But
importantly, near field antennas are more predictable to tune than
far-field antennas. For example, on a capacitive antenna with a
voltage driver or an inductive antenna with a current driver,
extending the size of the antenna, will invariably increase field
or range and increase loading on the driver. On a Far-Field system,
increasing antenna size often degrades radiation efficiency in a
non-intuitive manner.
[0058] Depending on the coupling, noise environment, and used
model, near-field systems either use baseband data or modulate data
on an RF (Radio Frequency) carrier. For baseband data, the
transmitting antenna is driven directly by the serial data without
carriers.
[0059] Far-field radio systems almost always use a carrier to deal
with the strong frequency dependent amplitude and phase shifts
arising from the far field propagation characteristics. In order to
use baseband for far field communication requires extensive signal
processing and dynamic characterization (training) to overcome the
propagation path's highly variable effect on phase, time and
frequency distortion of the signal. Historically, since dominant
radio technology has always been far field, it is normal practice
to apply far-field radio techniques to variable distance, large
dynamic range near-field systems since the technology works very
well without modification for near field. Consequently, if the
antenna geometry is variable or if free space distance and
orientation is variable, near-field systems are generally seen as a
type of short range RF system and standard practice is design it as
a standard radio system using a modulated carrier.
[0060] Although near-field systems don't have far field propagation
impairments that are normally resolved with carriers, another
reason for carriers instead of baseband is to deal with frequency
dependent phase shift and delay arising from multi-stage
amplification and gain control. Any variable distance radio system
whether near-field or far-field typically has a 100 dB or more
dynamic range between the noise floor and the maximum input signal
level. In order to provide very large amplifying gain and to allow
for gain control, radio receivers generally use several AC coupled
bandpass amplifiers. Multi-stage amplifiers are especially
necessary to achieve 100 dB of gain at very high frequency since
gain of most amplifying circuits decrease with increasing
frequency. Band pass amplifying creates significant non-linear
phase shift outside of the amplifying band that would make
demodulating a baseband signal very difficult. Simple window or
hysteresis baseband demodulation requires a 6 dB per octave rolloff
below the low frequency response corner to a frequency that is at
least three times lower in frequency than the corner to prevent
excessive under or over shoot. Excessive under or over shoot can
cause spurious detection or shift the detect level on subsequent
pulses, a type of inter-symbol interference.
[0061] In addition, for regulatory reasons, most radio systems use
modulated carriers as a way to constrain the radiated power to
certain approved narrow frequencies or bands. In general, baseband
transmission is not allowed for far field radio. Again, since
dominant radio systems can't use baseband, the use of baseband in
variable range near-field systems is contrary to standard
practice.
[0062] However, one problem with high frequency carriers on wider
band near field systems is that there is a higher likelihood of
violating regulatory radiated limits, especially if the data rate
happens to be low. As the carrier frequency increases, the far
field radiation power increases with the fourth power of the
distance. The carrier bandwidth can be spread, helping to reduce
the energy in a any single band below regulatory limits if the data
modulation is sufficiently wide, typically above several Mbps. Low
cost carrier based data systems typically need to use a carrier
that is at least twice to ten times the data rate in order to allow
simple modulation and demodulation techniques. Consequently, at 500
Mbps, a low cost nearfield carrier system, would require a carrier
of 1 GHz to 5 GHz. Baseband systems don't have this issue since far
field radiation does not arise from the static near fields but only
from the change that is the edges of the baseband data. As the data
rate goes up, the far field radiation also goes up proportionally
but if the data is pseudo random, not having high percentage of
repeating patterns, then the radiated signal is spread over a wide
bandwidth with the energy per root/Hz relatively constant. The
latter has a better likely hood of passing regulatory limits that
tend to be structured in terms of peak power per given bandwidth.
Consequently, for very high speeds, near-field baseband systems
have advantages over carrier systems.
[0063] On large dynamic range systems that use AGC, offset that
arises from fast AGC attack is generally a non-issue on carrier
systems but a serious problem on baseband systems. Normally, when
automatic gain control is applied in response to a signal, it will
create significant amplitude low frequency offsets or spurious
transients that can cause overload or signal distortion. On carrier
systems these are normally blocked from being amplified by the low
frequency roll off of each cascaded AC coupled bandpass amplifier.
On a baseband system in order to achieve high gain while rolling
off the low frequency corner at 6 dB per octave requires cascading
DC coupled amplifier stages with a single pole gyrator type bias
feedback. In such a system, when AGC causes attenuation within the
gyrator loop, the low frequency corner moves downward in frequency
as a function of the drop in loop gain. Since offsets created when
the gain changes can be amplified to large values and because the
gain around the loop drops, it increases the offset settling time
causing signal distortion or bit errors. Conventional wisdom is
that baseband is not suitable for the larger 100 dB dynamic range
of any variable distance RF system whether near-field or
far-field.
[0064] Of course the above offset problem can be avoided if AGC is
not used within the loop on a baseband system. For 20 dB dynamic
range where noise is significantly below the minimum detect
threshold, AGC is not required. In all large dynamic range systems,
AGC is necessary to create noise quieting, since by increasing the
signal level, the gain is reduced, lowering the noise floor until
sufficient signal to noise is achieved. Practically, for proximity
communication systems, this means that a user moves the
transceivers closer to each other until signal quality comes up
enough for reliable communication.
[0065] Practically, capacitive baseband near-field systems
typically have less than 20 dB dynamic range because coupling
geometry is fixed, distances are less than a few millimeters,
typically through non-air dielectrics, and environmental noise is
low. These systems use capacitive baseband as a method to provide
high voltage isolation or contactless communication such as between
ICs or across circuit boards. In these uses, because the antenna
geometry is fixed, they are seen as capacitors, albeit inefficient
ones.
[0066] Despite their limited dynamic range, these capacitive
baseband systems can operate close to the maximum switching rate of
the current technology, which is a key reason they are being
explored for inter-chip communication. Another advantage of
capacitive baseband transceivers is that higher speed transceivers
are transparently compatible with lower speed transceivers. They
can communicate at their highest common data rate. Commonly,
carrier systems must change carrier frequencies or modulation in
order to change data rates.
[0067] Where variable distance capacitive baseband communication
between devices with floating grounds is desired, conventional
wisdom is that a differential capacitive antenna and receiver needs
to be used. (U.S. Pat. No. 6,336,031, Schyndel). Even if a ground
is present, differential antennas in the base band are seen as
necessary due to large common mode ground noise, common mode field
noise (from large electrostatic noise generators; such as, compact
fluorescent lights, computer monitors, etc.). However, a limitation
of a differential capacitive baseband system is the need to align
the transmitter and receiver antennas to prevent polarity ambiguity
unless a polarity independent coding scheme is used. Another
limitation is that range is a highly variable function of
alignment.
[0068] Longer ranges require significant gain making the systems
vulnerable to noise. Noise can be reduced with bandwidth filtering,
but on a baseband system, more orders of filtering than provided by
a first order differentiated response causes signal overshoot,
undershoot, or ringing, making data demodulation difficult.
Modulated carrier systems don't have this issue. Generally any of
the standard carrier RF amplifying or filtering circuits will cause
these problems when used on baseband signals.
[0069] Another problem on high gain baseband systems is capacitive
or inductive feedback from the receiver data output. On limited
dynamic range systems with fixed antenna geometries, feedback
coupling is normally more than 10 dB below the minimum receive
signal and some positive dynamic feedback is desirable to provide
hysteresis, good for eliminating unwanted slow edge transitions.
However, on high gain variable distance systems receiver data
output can be the largest digital noise source picked up by the
receiving antenna since the receive output is often much closer to
the antenna than the desired signal source antenna. Modulated
carrier based RF systems are generally less vulnerable to this
noise by limiting the slew rate or frequency response of the
digital receiver output and by using a carrier above this
frequency. Then bandwidth filtering can eliminate any disruptive
feedback. However, as explained earlier, baseband systems cannot
use a bandwidth filter with more than 6 dB per octave rolloff. This
is another reason high gain RF baseband systems have not been
considered viable.
[0070] One of the standard wireless short range methods for
communication is far-field radio such as IEEE 802.11 data
transceivers. Although these systems are effective communicating at
ranges less than one meter, they are at least ten times more
expensive than a baseband near-field system because they were
designed for 100+ meter range and must meet certain regulatory
frequency band operating requirements due to their higher radiated
output. RF systems in development that will exceed 100 Mbps at 100
meter range will be even more expensive. A significant cost of any
integrated far-field radio system is the very specialized antenna
engineering efforts required for each product design-in.
[0071] It is the engineering efforts and cost of antenna design
that makes shorter range and lower cost far field radio systems
impractical. Although it is possible to build a one to three meter
range far-field radio system that operates below regulatory
radiated power limits, that eliminates expensive frequency
determining components, that has wider bandwidth, and that uses
simpler data modulation techniques, it also requires careful
antenna engineering in order to achieve ranges in excess of a
comparable data rate near field system. At one meter range, under
regulatory limit far-field systems that transmit data faster than
100 Kbs only have about 30 dB of margin between noise floor and
maximum signal. Since transmit radiated levels should be about 10
dB below regulatory limits to ensure safe regulatory conformance
over normal production variation, this leaves only 20 dB margin
above the receiver noise floor. If the antenna has more than 20 dB
of loss over a dipole, then range will fall below one meter. Since
most systems use the same transmit and receive antennas, this means
that the receive antenna must have no more than 20 dB loss, and in
transmit mode the antenna must have fairly predictable gain,
perhaps with no more than +-6 dB gain variation. Both of these
requirements can only be satisfied by proper antenna design and
validation in the end product. These are significant cost
impediments over existing IrDA transceivers. In addition, any
efficient antenna even at 2.4 GHz, consumes significant printed
circuit board area or must project from the case. If a customer is
to incur these antenna engineering and size costs, they might as
well spend a bit more for a wider connectivity, longer range IEEE
802.11 or Bluetooth system.
[0072] Near-field antennas are simple and don't have the costs of
far field antennas. A key advantage of a small (<<half
wavelength) near-field antenna, is that it can be driven harder to
produce a larger near-field than the near-field from a larger more
efficient radiating antenna. Near-fields from a small antenna fall
off at a rate much faster than propagating far-fields. The
near-field produced is fairly independent of frequency as long as
the antenna is smaller than the half wavelength. To a first order,
near-field electrostatic coupling is proportional to antenna
surface area and inductive coupling is proportional to the loop
area. Low frequency roll off is a predictable function of the
receiving near-field antenna termination resistance. All of this
means that near-field over short ranges can provide good signal to
noise at very wide bandwidth without strict regulatory constraints
and can be flexibly installed in a wide range of products without
critical antenna engineering necessary for far-field systems.
[0073] Near-field communication devices are seen as having a good
potential for short range, secure data transfer applications
traditionally served by IrDA. Only recently with the advent of low
cost, high density memory, suitable for handheld devices, has need
arisen for low cost, very fast file transfer communication systems.
However, due to the previously described factors, variable range
modulated carrier based near-field transceivers have not been
considered to be a competitive improvement over lower cost, higher
speed, and smaller IrDA devices. Due to competition from Bluetooth
and WiFi, the somewhat lower cost of existing RF ID based
near-field carrier systems hasn't overcome their handicap of
limited range and limited data rates. Very high data rate baseband
capacitive near field systems are not seen as capable of variable
range necessary for proximity communication.
[0074] Although high speed, short range near-field transceivers in
electronic devices might be desirable, like any new communication
protocol or medium, achieving market success has always been
extremely difficult since there is no installed base of
applications or compatible near-field transceivers to allow new
adopters to immediately use their product. Any new application
competes against entrenched alternatives notably existing wireless
technologies. Superior performance and lower cost of a new
communication technology is no guarantee of quick market
acceptance. More typically, any new communication media may take
5-10 years for market penetration.
[0075] Part of this slow acceptance of any new communication medium
is because any new physical layer transceiver requires significant
investment changes in product software and hardware. This is a high
risk business development if it is unclear whether there will be a
market acceptance and return on investment. With modern
communication ICs, although the silicon fabrication cost of a
transceiver may only be ten cents, the development costs may exceed
millions of dollars. To recoup these investments requires a minimum
market success of tens of millions of devices sold within five
years.
[0076] For example, one problem of adding a near-field transceiver
in an electronic product is that the antenna may require
modifications to the product's case. Many electronic products have
a conductive shield inside of their case to minimize EMI radiation.
Although this case shield provides a good antenna return for the
capacitive near-field transceiver, a separate field plate needs to
be either added to the case or if an antenna on a circuit board is
used, then a hole in the case shield needs to be provided and the
antenna must be placed close to hole. For inductive near-field a
loop must be provided for in the shield or slots cut in the shield
so that a circuit board loop can radiate magnetic fields without
excess eddy current losses because of the case shield. Although
less than far-field systems, these are antenna costs that need to
be incurred to use a near-field communication.
[0077] In one exemplary embodiment of the present invention, a high
data rate, low cost 0-10 cm near-field baseband transceiver is
added to an IrDA transceiver IC. Further embodiments call for
combining a near-field baseband transceiver or receiver compatible
with the IrDA/Near-Field transceiver with any standard far-field
wireless data system or a wired data communication system. The
near-field transceiver only adds about 20-50% increase in IC area
or cost over the IrDA only transceiver. When combined with other
wireless or wired transceiver systems it adds an even smaller
increment in cost, yet yields a significant enhancement in secure,
high speed bridging and file transfer communication. The near-field
may be also integrated on chip with other RF wireless transceiver,
like IEEE802.11x, Bluetooth or Zigbee.
[0078] The IrDA/Near-Field transceiver has two operating modes 1) a
0-500 Mbps 0-10 cm range near-field baseband mode and 2) any of the
standard IrDA speeds 115.2 Kbps, 1 Mbps, 4 Mbps, or 16 Mbps. Both
modes are compatible with standard IrDA modules and controllers.
This dual-mode transceiver, similar to the reasons for dual and
tri-mode cell phones, allows a ready method to grow an installed
base of a new higher performing wireless communication standard
while staying back compatible with the existing IrDA installed
base.
[0079] The use of IrDA/Near-Field data transceivers may provide a
number of benefits depending upon the particular application. For
example, data speed may increase by approximately 100 fold at 0-10
centimeter range over either IrDA or RF Wireless and may increase
10 fold over IEEE 802.11g. A wider proximity communication arc may
be obtained than the +-15 degree IrDA cone. A shorter range,
secure, well defined proximity range may be obtained rather than
the large ambiguous range of Far-Field RF.
[0080] An IrDA/Near-Field device may have less than 1/10 the cost
of 11-54 MHz 802.11 or 1 MHz Bluetooth with less than a 20-50%
increase in the already very low cost IrDA transceiver. It may be
possible to obtain rapid, low cost product design-in for
IrDA/Near-Field because it is compatible with IrDA controllers from
115.2 Kbps to 16 Mbps. Further, the data stream transmit, receive,
and half duplex turn around are essentially transparent. Also, IrDA
high speed mode switching may be transparent when near-field
transceivers are combined with a 115.2K IrDA transceiver.
[0081] In IrDA/Near-Field applications, no separate antenna is
required and no special hole or modification to an electronic
product's EMI shield required for shield antenna since the IrDA
plastic infrared window is non-conductive. For Near-Field antennas
combined with standard RF wireless or wired communication systems,
the near-field antenna is simpler and easy to add to the Far-Field
system. Further, IrDA/Near-Field implementations may be compatible
with existing IrDA modules so that only minor circuit board changes
may be necessary.
[0082] Near-field generally provides high security from
eavesdropping beyond its 10 cm range. Even higher security (0-3 cm)
may be obtained by transmitting just from the shield or a smaller
transmit antenna. In near-field baseband mode, the transmitter
radiates a fixed energy per bit, providing a constant radiated
power per Hz independent of the data rate. This maximizes signal to
noise while staying under regulatory radiated limits. The high
speed near-field baseband mode may be backward compatible with
lower speed IrDA transceivers. By being backward compatible, new
near field IrDA transceiver may be able to "piggyback" onto high
volume IrDA production and deployment, which facilitates rapid
building of an installed base of a higher performance alternative
to IrDA.
[0083] IrDA/Near-Field or near-field may also be interfaced to the
Universal Serial Bus (USB) to allow low cost, high speed bridging
to the dominant USB short range wired data system. Further, a large
installed base of IrDA/Near-Field devices in cell phones may make
it desirable to install compatible Near-Field transceivers with
other wireless and wired transceivers. Also, IrDA/Near-Field may
provide a simple method to synchronize wireless communication
systems, either by mutual transfer of pairing data or by simple
simultaneous flagging. Still further, near-field may provide a
better audio link between a cell phone and a hearing aid and a
simpler method to upload hearing aid coefficients.
[0084] FIG. 1 illustrates an IrDA transceiver module with a metal
shield that is 7.3.times.1.9 millimeters. Since IrDA transceivers
are placed on the PC board edge to allow access to a plastic
infrared transparent window, the IrDA transceiver shield can be
used as an antenna for the near-field data circuit integrated in
the module's IrDA transceiver IC. In the near-field mode, the
infrared window acts as a proximity aiming mark since the module
shield is behind this window. If the product case has an
electro-magnetic interference (EMI) shield, then the window
provides a non-conductive hole for fields to escape. By using the
metal EMI shield as an antenna, an IrDA module vendor can use the
dual mode IrDA/Near-Field integrated circuit (IC) in an existing
IrDA module with little or no changes. In IrDA mode, the shield is
grounded inside the IC. In near-field mode, the shield is connected
to either the transmitter or receiver depending on the half duplex
communication direction. The antenna shield may be configured as
either a single ended capacitive antenna or an inductive
antenna.
[0085] FIG. 1 is a diagram illustrating a communication link having
two devices, where each device includes an infrared transceiver and
a near-field transceiver that utilizes a capacitive near-field
antenna. In FIG. 1, a transceiver devices 20 and 40 are
encapsulated in clear plastic cases 10 and 30, respectively, that
permit infrared transmission and reception of infrared data signals
via infrared lenses 22 and 24 for transceiver 20 and lenses 42 and
44 for device 40. Transceivers 20 and 40 also have near-field
transceiver functionality for exchanging data via capacitive
near-field antennae. In the example of FIG. 2, a capacitive
near-field antenna for transceiver 20 is realized by electrically
coupling an antenna input of the transceiver 20 to a shield 26 for
the transceiver. Likewise, a capacitive near-field antenna for
transceiver 40 is realized by electrically coupling an antenna
input of the transceiver 40 to a shield 46 for the transceiver.
When transceiver devices 20 and 40 are placed in close proximity to
one another, the transceivers are able to exchange data through the
use of near-field or radio frequency (RF) electro-magnetic signals
12 and 32. Note that the transmit data inputs to transceivers 20
and 40 may be coupled to their respective external shields 26 and
46 in an embodiment that employs baseband data transmission, in
which case the signal applied to the transmit data input is used to
drive the external shield as a capacitive transmit antenna.
[0086] FIG. 2 is a diagram illustrating a communication link having
two transceiver devices 120 and 140. Transceiver device 120
includes an infrared transceiver and an inductive near-field
transceiver that utilizes an auxiliary inductive loop antenna for
transmitting a baseband data signal. Transceiver device 140 also
has its transmit data input coupled to the external shield 46 to
illustrate that the external data shield may alternatively be used
as a capacitive antenna to transmit a baseband data signal. In the
example of FIG. 2, of the transmit data input of transceiver 120 is
electrically coupled to one end of an inductive loop antenna 122.
The other end of loop antenna 122 is coupled to a circuit ground
through a resistor. A grounded eddy current noise shield 124 may be
included to reduce the effect of internal field noise caused by
devices external to the transceiver 120, such as a controller.
Similarly, an output of transceiver 140 is electrically coupled to
one end of an inductive loop antenna 142 with the other end of loop
antenna 142 coupled to a circuit ground. A grounded eddy current
shield 144 may also be included. In one example of operation, data
transmitted by transceiver 120 via the loop antenna 122 is received
by transceiver 140 via shield antenna 46.
[0087] A near-field transceiver compatible with an IrDA/Near-Field
transceiver may also be a useful addition to other RF communication
data systems both as a way to achieve higher data rates than the RF
system and as a way to securely transfer data over short distances.
A very short range baseband near-field data transceiver system is
even lower cost than an IrDA communication system. The shorter
range of the near-field system is more secure than the longer range
IrDA system. At very short ranges of less than 1 cm, the capacitive
near field system can be very simple, without high gain, broadband
amplifiers, and automatic gain control (AGC). Its cost is so low
that combining it with another system may be a minor design-in
cost. It provides complementary benefits to other wireless
communication systems both in synchronizing pairing and higher
speed file transfer speeds, but it may also provide low cost
bridging between wired systems, such as USB, and other near-field
systems.
[0088] Including a low cost Near-Field system in an IrDA module may
drive acceptance of a compatible near field system in other
wireless and wired data communication systems by rapidly increasing
the installed base of products. Notably, the inclusion of an
IrDA/Near-Field transceiver in cell phones in lieu of the IrDA only
module may be an effective way to increase the near-field
transceiver installed base because the cell phone market is large
in size and geographic scope and has high product turn over
rates.
[0089] A differential capacitive antenna in baseband applications
is normally assumed to have superior noise immunity due to its
ability to reject common mode signals. In practice, it provides
little benefit due to the asymmetry of most internal electrostatic
noise sources.
[0090] Single ended antennas work by using the bulk of the product
as the return antenna. Many engineers assume that ground noise or
common mode environmental noise would make a single ended
capacitive solution excessively noisy. While it is typically true
that the external environment may present tens of volts of electric
fields from power lines, and common mode ground noise may also have
similar magnitude at frequencies to several hundred kilohertz due
to switching supply noise or power line transients, etc. However, a
key attribute of these environment signals is that they fall off
rapidly with increasing frequency due to the effects of
Electromagnetic Compatibility (EMC) regulation (see FIG. 10 of
Recommendation ITU-R P.372-8). At low frequencies, these near-field
signals, although large, do not propagate due to the poor radiation
efficiency of the fractional wavelength antennas formed by
electrical conductors, while higher frequency signals that might
propagate are filtered or attenuated to prevent propagation.
Because radiation efficiency increases with the fourth power of the
frequency or 12 dB per octave, near field digital noise from modern
electronic products needs to fall off at a similar rate to prevent
radiation in excess of regulatory limits.
[0091] Consequently, a single ended, capacitive near-field receiver
can reject the large amplitude, low frequency, signals while
communicating at the higher frequencies. By terminating with the
correct impedance, the antennas themselves can provide a 6 dB per
octave attenuation with decreasing frequency below the maximum
frequency of the system, rejecting virtually all of the lower
frequency common mode and environment noise. A second order high
pass filter can be added to further reject the lower frequencies.
If any second or higher order high pass filters are used it is
important that their low frequency corners are at least three to
five fold below the dominant high pass filter, in order to minimize
undershoot.
[0092] The dominant local electrical noise near any electronic
product is due to near-fields generated by its own active
electronics. For these noise signals, the pickup from a single
ended antenna is virtually the same as a differential antenna since
most of these local noise signals have a very strong gradient.
[0093] In many high speed electronic products the dominant near
field noise tends to be inductive because ground planes and case
shields tend to perform better as electrostatic shields than as
inductive eddy current shields. Unwanted far field radiation is
mostly correlated with high frequency currents on circuit board and
ground plane gradients due to high frequency inductive effects.
Consequently, in many products, the electrostatic high frequency
near fields are lower than the inductive fields, making a
capacitive near field system less susceptible to noise pickup than
an inductive near-field system.
[0094] Another problem with the use of a differential capacitive
antenna in baseband applications is that it suffers from phase
ambiguity requiring correct orientation between the two devices
that are communicating. The single ended capacitive technique has
the advantage that the signal polarity is always phased the same if
both near-field antennas are in proximity to each other. Similar to
a differential capacitive system, inductive near-field is only
phased correctly if the loops face each other. If the loop antennas
are proximate but misaligned to one side, a phase reversal may
occur. The reversal can be remedied by either the software or the
receiver hardware protocol automatically flipping the data phase.
For transparent IrDA compatibility, the capacitive technique is
simpler since it requires no phase adaptation of the protocol. For
example, in order to adapt a high speed serial protocol for phase
inversion, the beginning frame preamble sync byte detector can look
for both polarities of the sync bytes. If it gets two correlations
in a row of one phase, then that phase is assumed to be the correct
phase for all subsequent bits in the frame.
[0095] One significant issue with using the IrDA shield as a
capacitive or inductive antenna in a high sensitivity baseband
system is that the antenna shield may couple to the receiver output
causing serious feedback. This feedback is identical to IrDA
receiver output to photodiode input capacitive coupling.
Consequently, the same feedback mitigation methods used on IrDA
transceivers disclosed by Holcombe in U.S. Pat. Nos. 5,864,591 and
6,240,283 can be used.
[0096] Antenna Enhancements If the module manufacturer wants to
make no changes to their module design, then the new input/output
(I/O) needed for the antenna or antenna shield connection can be
scavenged from other existing module I/Os. For example, many IrDA
transceivers have a dual transmit input, one for high LED transmit
current and one for low LED transmit current. One of these inputs
could be sacrificed to allow the same pin count module to be used.
Or, existing I/O can be multiplexed with various schemes to free up
one or more pins without sacrificing existing functions.
[0097] To use an existing IrDA module design for IrDA/Near-Field,
the printed circuit board (PCB) that the module is mounted on would
typically need to be slightly modified since the shield is normally
soldered to the PCB ground. When used as a capacitive antenna, the
circuit board shield solder tabs would not be grounded on the PCB
but would need to be tied to the antenna I/O pin of the module.
[0098] For an inductive near-field antenna, different PCB
connections are made, one end of the shield is tied to ground and
the other end is tied to the antenna I/O pin on the module. Another
advantage of not directly tying the shield to an active pin on the
module, is that it allows the option of connecting the antenna IO
pin to a completely different antenna; such as, a field plate on
the case or a longer trace on the printed circuit board, for
example.
[0099] If the module manufacturer makes changes to their module,
then they can add extra pins to the module or make the antenna I/O
an internal connection to the shield via a mechanical contact,
soldering the contact to the shield or by capacitance between
shield and a large area trace on the module. The internal shield
connection would allow an IrDA/Near-Field module compatible with
existing PCB layouts. One problem with a mechanical pressure
connection between shield and module is that it may not maintain a
reliable ohmic connection over time. To remedy this, the
manufacturer might need to solder the metal shield to the module
contact. This adds a cost to the manufacturing process, but is
effective for both capacitive and inductive antenna configurations.
In the inductive configuration, one solder tab on the shield would
normally be tied to ground.
[0100] For a capacitive antenna configuration, a lower cost method
to couple the shield to the antenna input without soldering is to
use a capacitor formed between the metal shield and the printed
circuit on the back side of the module. If the back side of the
board has a conductive plane over a large area of the capacitor and
if the shield extends over this area making a flat close fit, even
if there is not a good ohmic contact, there can be enough coupling
capacitance to drive the shield with little attenuation. Because
the coupling between the shield and the surrounding ground or
module conductors may be less than 1 pF, only about 1-3 pF of
capacitance may be needed to couple to the shield. In IrDA mode,
when the antenna input is grounded, the shield would then be
grounded through several picofarads. This still provides effective
grounding for the very low noise charges picked up by the shield.
Typically, capacitive coupling to the shield from local digital
signals is less than several femtofarads allowing field attenuation
by about a thousand fold even though the photodiode coupling to the
shield may be thirty times greater than to the signal source. The
net effect is still a significant drop in coupled noise to the
photodiode input.
[0101] Some IrDA modules don't have shields. In this case, an
antenna on the printed circuit board that runs in front of module
will generally give good performance, whether the antenna trace is
used as a capacitive or inductive near-field antenna. However, the
shield may be a better antenna than the same size printed circuit
trace for either near-field capacitive or inductive mode. This is
because the IrDA module shield is typically spaced further from the
board ground plane and conductors that both act as signal shields
and also create near-field noise. Consequently, the IrDA shield
near-field antenna may tend to have a better signal to noise than
the printed circuit trace near-field antenna of the same size.
[0102] An improvement against local field noise is to add a noise
shield (different than the module shield) behind the
IrDA/near-field transceiver module. An example of this approach is
demonstrated in the shields 124 and 144 of FIGS. 2 and 3. This
shield can be a ground plane on the surface of the board. This
local noise shield reduces pickup of both electrostatic and
magnetic noise near-fields from other active signal lines on the
printed circuit board. However, it is important that this noise
shield be close to the noise sources but as far as practicable from
the shield antenna since it will also act as a shield against
desired signals if is placed too close to the shield antenna.
[0103] Another enhancement to improve the range of the near field
device is to augment the shield antenna with a larger auxiliary
transmit antenna. This can be accomplished either by making sure
that the IrDA shield driver is the same phase as the transmitter
input in baseband mode, and then driving the separate auxiliary
antenna with the same transmit signal input, as demonstrated by the
transceiver 120 connection to antenna 122 in FIG. 2, or by adding a
separate auxiliary transmit antenna driver pin on the module, as
demonstrated by the connection of transceiver 140 to antenna 142 in
FIG. 2. For carrier mode, the auxiliary antenna would preferably be
driven from a separate module pin if not tied to the shield. See
FIGS. 4 and 5 for examples of drive circuits. The auxiliary
transmit antenna can also be in several different sections to allow
transmitting from several different hotspots on the product.
[0104] Typically, the auxiliary transmit antenna 122 or 142 would
be a longer trace run around the edge of the product but it might
also be a larger plate or conductive trace on the inside of the
case. During transmitting, both the shield antenna 26 or 46 and the
longer transmit antenna 122 of 142 would be driven. During
receiving, only the shield antenna 26 or 46 would be used. The
larger auxiliary transmit antenna 122 142 may increase the
near-field range by up to ten times or more. It is still desirable
to use the small shield 26 46 as a receiving antenna, whether
configured in capacitive or inductive mode. Making the receiving
shield antenna larger would typically have no benefit, since the
local noise generated by the product circuitry or nearby devices
will usually be larger than the receiver amplifier noise. In
addition, a small antenna, e.g. the size of the IrDA module shield,
is easier to shield (as discussed above) from internal fields than
a larger antenna, which will have proximity to a larger number of
local noise sources. Consequently, increasing the size of the
receive antenna may increase pickup of field noise even more than
the increase in the receive signal. However, increasing the
transmit antenna size increases the transmit signal field relative
to the field noise. For example, an IrDA/near-field transceiver 120
140 might be placed in the corner of a cell phone to allow easy
placement of the corner with respect to another IrDA/near-field
device. In this example, the transmit antenna 122 142 might be
placed around this corner to increase the range, e.g. on the order
of three times or more.
[0105] Similarly, to increase the range of an inductive mode
IrDA/near-field transceiver, a larger transmit (TX) loop antenna
can be used while the shield loop can be used for receiving. About
the same signal to field noise improvement occurs as with the
electrostatic mode by use of the larger TX antenna. If the TX input
driver is used, as shown in the connection of transceiver 120 to
antenna 122 in FIG. 2, then the TX loop antenna 122 can be driven
through a resistor to limit the current so that the TX input has
sufficient voltage to drive the near-field transmitter.
[0106] In the embodiment of transceiver 120 and antenna 122 shown
in FIG. 2, the loop antenna current limiting resistor is disposed
at the ground end of the loop, in which case the TX antenna will
act as both an electrostatic and inductive antenna. This allows the
receiver circuit to switch between inductive or capacitive antenna
mode depending on whichever gives a better signal to noise ratio
against the local near-field noise. Of course, this would typically
require more I/O pins to switch the antenna from a loop to a
capacitive antenna.
[0107] Even if a larger separate TX antenna 122 142 is used, it may
be desirable to have a short range security mode where only the
shield 26 46 is driven by the transmitter. With only the IrDA
module shield driven, the communication range would be limited to
within less than 3 cm of the shield. This is because the near-field
transmitter range is generally a more predictable function of
transmitter antenna size and driven power. Since security breach is
often a result of unwanted transmitter pickup, the transmitter of
secure information can limit the valid receiving region to a small
volume by limiting the transmitting antenna size and power.
[0108] IrDA/Near-Field Transceiver Integration: Another advantage
that may be obtained from combining IrDA and a near-field
transceiver is that the near-field transceiver can operate
half-duplex in almost exactly the same way as IrDA. In half-duplex
operation, both transmit and receive is possible, but not at the
same time. Half-duplex in transceivers lowers the cost and
implementation complexity by using the same frequency or bandwidth
in both communication directions and avoids transmit to receiver
overload or interaction.
[0109] A 115.2 Kbps IrDA with a near-field dual mode transceiver
may be made transparent to many 4 Mbps or 16 Mbps controllers. The
reason is that IrDA transceivers above 4 Mbps, and some above 1
Mbps, typically have a speed mode switch that selects between low
speed, usually 115.2 Kbps, and higher speeds. A 115.2 Kbps
transceiver with an integrated near-field transceiver could switch
to near-field transceiver mode when the controller tells it to go
to high speed mode. Of course, at 115.2 Kbps, the IrDA range may be
in excess of one meter, while for near-field, the range would be
reduced to merely several centimeters. During the 115.2 Kbps IrDA
exchange, the software systems of both products normally
communicate their capabilities. If they both had compatible
near-field transceivers, they could prompt the users to place both
infrared windows within several centimeters to allow very high data
transfer rates.
[0110] Since IrDA transceivers above 1 Mbps already typically
include a speed switch, it may be useful to add another switch mode
for near-field. In fact, depending on the specific communication
application, it may be desirable to have several different
near-field modes. Some of these may be different data rates,
sensitivity or transmit levels. Most IrDA transceivers switch
speeds by using the SD pin to clock data on the TX input pin. The
falling edge of SD is used to clock the data value on the TX pin.
Although the falling edge of the SD enables the part, the TX input,
if asserted, has no effect until it first returns to the TX disable
state. This prevents transmit glitches while performing the speed
serial shift programming. This scheme can be extended to shift a
number of bits for other control states. Optionally, the internal
shift register bits may be returned to a default value after some
minimum amount of time that SD has not been toggled. This avoids
the requirement of shifting all bits into the shift register every
time a mode change occurs.
[0111] Half duplex turn around, i.e. going from transmit to receive
or receive to transmit, on the near-field transceiver can function
similarly to IrDA where the unit is normally in an idle receive
state unless a transmit signal occurs, which immediately disables
the receiver with or without transmit echo. When transmitting
stops, the receiver recovers after some short latency period. With
a high speed RF receiver, the transmit latency, i.e. the time that
the receiver requires to recover from the transmit signal over
load, can be much faster than in an IrDA transceiver, where the
photodiode recovery can be tens of microseconds. A near-field
wideband receiver can typically recover in less than a few
microseconds.
[0112] Baseband innovations and carrier systems: The simplest and
highest speed near-field transceiver uses baseband data to transfer
data with a capacitive or inductive coupling. Both techniques are
well known in the art. Demodulating the baseband data
differentiated edges typically requires a type of low threshold
hysteresis receiver. Capacitive or inductive coupling has various
advantages and disadvantages depending on the performance
constraints of the environment. Both techniques could be
incorporated in the same module by adding a second pin to control
whether the shield is configured as a capacitive plate or inductive
loop.
[0113] Conventional experience is that modulated carriers,
typically with inductive antennas, are more flexible and perform
better than baseband, especially in capacitive mode, and that
baseband is not suitable for high gain or large dynamic range
systems. With the following modifications in circuit design, these
limitations may be overcome resulting in a very high data rate,
short variable range transceiver, that may be lower cost and
simpler than a carrier based near-field system.
[0114] The receive signal of the baseband data is the
differentiated edge of the transmitted data, since an antenna
cannot receive or output a signal from a static field whether
electrostatic or magnetic. The differentiated time constant is
proportional to the antenna terminating resistance on the
capacitive antenna or inversely proportional to the loop
terminating resistance on the inductive antenna. If these are the
principal time constants, then very little undershoot will occur.
Detection after amplification is via a comparator that flips state
when the incoming pulse of the correct polarity exceeds the detect
threshold above the quiescent reference level. Normally, positive
pulses will flip the comparator to one state while negative pulses
will flip into the other state. Subsequent pulses of the same
polarity will have no effect. Since noise can flip the detect
comparator to the wrong quiescent state, a circuit that restores
the detect comparator to the idle state after a period of time is
necessary. In this application, the restoring timer should revert
the detect comparator to the idle state in about 1 us to 20 us.
This allows quick recovery from noise, but allows the near-field
output to be compatible with IrDA protocol speeds including the 9.6
Kbps initial discovery speed. Faster recovery may shorten valid
data pulses possibly causing data errors.
[0115] FIG. 8 is a transistor diagram illustrating an exemplary
embodiment of a receiver circuit for use with a capacitive
near-field transceiver device. FIG. 9 is a transistor diagram
illustrating one exemplary embodiment of a comparator circuit in
the circuit of FIG. 8 for detecting a received signal. FIG. 10 is a
transistor diagram illustrating one exemplary embodiment of a
multiplexor circuit in the circuit of FIG. 8. FIG. 11 is a
transistor diagram illustrating one exemplary embodiment of a bias
current generating circuit in the circuit of FIG. 8.
[0116] The transceiver circuit 500 of FIG. 8 includes a comparator
510 having a non-inverting input electrically coupled to external
interface pin RXCAP for receiving a data signal. Comparator 510
compares the signal received via pin RXCAP to an analog ground
signal input at external interface pin GNDCAP, which is typically
capacitively coupled to a circuit ground potential. Comparator 510
compares the received data signal to the analog ground signal to
generate a digital output signal that is output from transceiver
circuit 500 via external pin ADC_OUT. FIG. 9 is a transistor
diagram illustrating one example of a comparator circuitry suitable
for use as comparator 510 of FIG. 8.
[0117] Biasing for transceiver circuit 500 is provided by biasing
circuit 512, which converts a reference current input via external
interface pin IBP_10U to the biasing current signal needed to bias
the circuitry for operation. FIG. 11 is a transistor diagram
illustrating one example of a biasing circuitry suitable for use as
biasing circuit 512 of FIG. 8.
[0118] A multiplexer 520 is used to set transceiver circuit 500
into either an operational mode or a loop-back test mode. If the
TST_SEL interface pin is set to a "1", then the signal output by
comparator 510 is selected for output to the TXCAP pin, which
drives an antenna. This results in the receive signal being looped
back and retransmitted. If the TST_SEL pin is set to a "0", then
the data signal input via interface pin DAC_IN is passed through to
the TXCAP pin for transmission. FIG. 10 is a transistor diagram
illustrating an example of multiplexer circuitry suitable for
application as the multiplexer 520 of FIG. 8.
[0119] In a capacitive near-field baseband data system, the total
current consumption during transmitting and receiving may be less
than one tenth of a comparable radio frequency link with similar
data rates. This is because the transmitting power is low and low
noise, high current bias amplifiers are not required. Also, complex
digital signal processing, VCOs, and mixers that are power
consuming are typically not needed.
[0120] With some added complexity to the near-field baseband
transceiver, switching between baseband or modulated carrier mode
can be implemented. In the carrier mode, data may be modulated on a
carrier frequency by use of one of a number of common modulation
techniques; such as, amplitude shift keying (ASK), frequency shift
keying (FSK), phase shift, etc. One solution to resolving the
phasing ambiguity on near-field inductive systems is to operate
them with a carrier. Also, in modulated carrier systems, because
they operate over a narrower frequency range, the receive signals
can be bandpass filtered to provide improved immunity against
near-field noise. With a modulated carrier near-field communication
system, the maximum data rate will typically be less than a
base-band system, but may allow ranges approaching 30 centimeters
while communicating at speeds faster than 16 Mbps.
[0121] A modulated carrier system can normally operate over a very
wide bandwidth and over frequencies not allowed for longer range
higher radiating systems, allowing use of lower cost,
lower-tolerance, on-chip frequency sources and filters. Generally,
any regulatory approved radio data system; such as, Wi-Fi IEEE
802.11, requires crystal controlled frequency sources.
Consequently, a modulated carrier based near-field system is
normally still significantly less costly than a longer range
regulated radio system. Therefore it may be desirable to combine a
near-field base band system with a simple modulated carrier system
that operates at lower data rate, all combined with an IrDA
transceiver. In such a tri-mode system embodiment, the base band
mode allows faster data rate transfer at short range and the
carrier mode will allow greater range than the baseband mode, but
at faster speeds than the IrDA mode.
[0122] It is typically desirable that these near-field receivers
have AGC (Automatic Gain Control), whether baseband or using
modulated carriers. AGC creates noise "quieting" by reducing
spurious noise detects as the signal increases amplitude.
Typically, AGC reduces gain so that the detect threshold is about
one half of the peak signal height to give a lower spurious detect
rate and better pulse width accuracy. In this application, it is
desirable that the AGC attack time occur in less than the high
speed protocol training preamble, usually a few microseconds and
the decay time should be long enough to hold up the AGC during the
longest string of no pulses that might occur in the data stream.
For high speed protocols above 1 Mbps, the no signal interval is
usually 4-8 bits or about 5-10 us. So, in 5-10 us it would
desirable that the gain would not increase more than about 3 dB.
This would allow AGC latency recovery of 40 dB drop in about 100
us. If a near field system has a 40 dB signal range, then this
means that the receiver will recover to maximum sensitivity in 100
us after receiving a maximum amplitude signal.
[0123] AGC provides quieting when signals are present. But when no
signal is present, the gain will increase as a result of no
detected signal and spurious detection may occur from near-field
noise in the environment. In principal, with some controller
designs this should not affect controller performance which looks
for the correct starting sequence of data and ignores random data.
However, if a controller has difficulties with excessive spurious
noise when a signal is not present, it would be desirable to set
the minimum detect threshold with an external component since the
near-field noise may vary between different types of products. This
allows the product end designer to adjust the minimum detect level
to increase the effective range without excessive spurious outputs.
Since input/output pins on IrDA transceivers are at a premium, with
typically only 6-8 pins used for all power and functions, some type
of detect adjustment multiplexed on an existing pin would be
desirable.
[0124] As pointed out earlier, rapid attack gain changes from the
AGC causes significant offset. This offset creates a significant
signal, especially with the high gain DC coupled amplifier with a
single pole gyrator type feedback. In order to remedy this, the AGC
circuit is typically balanced, but may introduce a small deliberate
offset at maximum attenuation that exceeds the worst mismatch. The
offset should be anti-signal (opposite to the direction or polarity
of the received signal) since the peak signal drives the AGC gain
control downward. Otherwise, if the offset is in the same direction
as the signal, then regenerative AGC attack will occur, causing AGC
overshoot. It is preferable that the gyrator feedback is applied
after the first gain control stage or attenuator so that the
gyrator low frequency corner does not move with the AGC stage.
[0125] In another embodiment, the circuit is provided with a
detector bandwidth that tracks the AGC level, which widens the
bandwidth as the peak signal level increases. For low level
signals, the detector bandwidth should be low, effectively lowering
the detection noise allowing the detection of weaker, lower data
rate signals. If the user needs to communicate at a higher date
rates, then the user can place the transceivers closer together,
which increases the signal level causing the AGC to increase and
the detector bandwidth to widen. This method automatically adapts
bandwidth for the signal level. However, depending on the local
noise frequency and amplitude characteristics, it is desirable to
allow the product designer of the end product to adjust the AGC
bandwidth threshold, which is the AGC level at which the detector
bandwidth widening starts to occur. The threshold should be set to
start at least 6 dB above the background ambient noise level in
order that the background noise not degrade the signal as the
bandwidth widens.
[0126] In order to set this AGC bandwidth threshold, the near-field
transceiver may have a separate pin for use with an external AGC
bandwidth threshold adjustment resistor. An advantage of the
dynamic control of bandwidth by signal level is that it allows for
low integrated circuit (IC) bias current when no signal is present.
While there is no signal present, the bandwidth will move to the
lowest frequency or data rate, which typically requires lower
amplifier and comparator bias and may be less than 100 uA. Only at
higher bandwidth will the idle current increase, e.g. by one or two
orders of magnitude, to allow wider bandwidths and faster data
rates. This is a desirable attribute since most communication
occurs in bursts with a low overall duty cycle, e.g. typically less
than 1%. This feature may allow the average current consumption to
be approximately two orders of magnitude lower than the current
consumption at the maximum data rate. The idle current consumption
may be lowered further by enabling the receiver at a low duty
cycle.
[0127] In another embodiment, the I/O pins for the adjustment
resistors for both the minimum detect threshold and the AGC
bandwidth threshold can be multiplexed with the antenna input and
the SD pin in order to avoid adding more pins to the transceiver
module. FIG. 3 is a diagram illustrating a communication link
having two devices, where each device includes an infrared
transceiver and a near-field transceiver that utilizes a capacitive
near-field antenna as well as an auxiliary transmit antenna and
adjustment resistors. In the example of transceiver 220 of FIG. 3,
an antenna pin is use to connect to a shield antenna and to an
adjustment resistor. In the example of transceiver 240, the SD pin
is used to connect a resistor for adjusting a detect threshold and
the antenna input is used to connect a resistor for adjusting a
detection bandwidth.
[0128] The antenna input can be multiplexed by coupling it to the
receiver amplifier input with a capacitor and then biasing the
antenna input pin with a voltage source through a resistor. By
tying an external resistor to ground on the receiver input, the
input voltage level or input current can be measured and used to
adjust the AGC bandwidth threshold. Typically, a lower voltage
level or higher current associated with a smaller resistor would
raise the AGC bandwidth threshold while also increasing the
rejection of low frequency noise components by decreasing the
antenna input time constant.
[0129] The SD pin can be multiplexed by placing an adjustment
resistor between it and the SD digital driver. Since SD is normally
driven to ground by a CMOS driver from the controller when the part
is enabled, then if the transceiver is in near-field mode, the
internal IC circuit can apply an internal voltage below the SD
logic switching threshold but above ground. Typically, this voltage
might provide a pull up to 0.4V, but from a unidirectional (diode
like) current limited source. The current level flowing from the SD
pin to the SD driver, set by the external resistor in series with
the SD pin and the SD driver, sets the detect threshold. If the SD
driver rises above the 0.4V level, then the SD input also rises
above the 0.4V level causing shutdown when it rises to about the
logic threshold, e.g. around 0.8V-1.2V. A minimum value set
resistor can be included internally in the IC, so that the extreme
sensitivity value can be set if the SD pin is directly driven
without an external set resistor.
[0130] It is also possible to reverse the functions of these two
adjustable resistors, so that the resistor on the antenna input
sets the minimum detect threshold and the resistor in series with
the SD pin sets the bandwidth offset.
[0131] In another embodiment, instead of using external resistors,
either of these parameters may be digitally adjustable by expansion
of the SD TX input serial shift function normally present on high
speed IrDA transceivers. This allows the shifting of a number of
bits into an internal shift register for programming these and
other parameters.
[0132] As noted above, a high speed near-field RF transceiver that
can operate in either baseband or carrier mode may be added to
products that currently use IrDA transceivers. A combined 115.2
Kbps IrDA transceiver with a 16 Mbps with a near-field transceiver
could be both lower cost and much smaller than a 16 Mbps IrDA-only
transceiver. Since 16 Mbps digital controllers have been available
for a long time at low cost, the new availability of a small, low
cost 115.2 Kbps IrDA/16 Mbps with a Near-field transceiver may
facilitate rapid replacement of both slower IrDA transceivers and
controllers. Quick development of higher speed controllers could
follow since low cost, 100 Mbps with near-field transceivers would
be available. Historically, next generation IrDA digital
controllers have been developed many years before a compatible
small, low cost IrDA transceiver becomes available.
[0133] Combining Near-Field transceivers with other Wireless and
Wired Communication Transceivers Adding the above described
near-field transceiver and related innovations to a standard
far-field wireless transceiver provides mutual benefits in three
application areas of high speed file transfer, wireless
synchronization, and security. First, a baseband near-field
transceiver provides higher data speed, e.g. one the order of
10.times. far-field wireless data rates, for file transfer at a
small increment in cost. Second, a baseband transceiver can provide
a convenient method for synchronizing paired far-field wireless
transceivers. Third, it can provide a secure method to transfer
encryption keys for longer range wireless communication systems. It
is desirable for the combined near-field and wireless system to be
compatible with a IrDA/Near-Field transceiver in order to exploit
the utility and facilitate the acceptance of this baseband
near-field method of communicating between electronic products.
[0134] Adding a near-field transceiver to wireless and wired
transceivers that is compatible with an IrDA/Near-Field installed
base may increase the utility of both systems by providing a low
cost, convenient, connector-less file transfer system between
desktop computers and portable battery powered, handheld products;
such as, cell phones, digital cameras, MP3 players, video players,
laptop computers, etc. The IrDA/Near-Field capacitive system would
provide a ready installed base.
[0135] When adding a near-field transceiver to a non-IrDA
communication system, there may not be a shield available for use
as an antenna. However, like the IrDA module without a shield,
antennas both small and large for both long range and short range
secure communication can be readily added to obtain some of the
performance features discussed above.
[0136] For pairing between two wireless transceivers, a baseband
near field system can be operated as either a short range
communication system for securely passing synchronizing data
between two far field wireless transceivers or as a relatively
simple proximity synchronizing flag. FIG. 6 is a diagram
illustrating an example of a near-field communication link between
a cell phone device and a Bluetooth headphone device for use in
pairing control. In the example illustrated, cell phone 400
includes an IrDA and Near-field pairing controller 410 that is
connected to transceiver 420 that is capable of both infrared and
near-field communication. Likewise, Bluetooth headset 430 includes
a near-field transceiver 440 having a near-field antenna 442 for
receiving the near-field signal transmitted by transceiver 420 of
cell phone 400. Headphone 430 also includes a pairing controller
444 that uses near-field transceiver 440 to communicate with
pairing controller 410 of cell phone 400. This arrangement allows
the near-field communication link between transceivers 420 and 440
to be used to exchange messages in a protocol for pairing the
headphone 430 to the cell phone 400. FIG. 7 illustrates an example
of an application of the pairing arrangement of FIG. 6, where the
headphone 430 is a hearing aid device.
[0137] When the near-field system is operated as a communication
link, a minimum level of protocol is required to support serial
communication between two devices. This allows for the safe
transfer of data without risk of eavesdropping, though with the
added cost of a serial communication controller or software stack
on the host microprocessor. If one side of the connection is
already an IrDA/Near-Field transceiver, then the IrDA controller
may transparently provide this functionality. However, if the other
side of the wireless connection does not have an IrDA controller,
then it may be necessary to add a controller or provide additional
software for the wireless controller, which may increase cost.
[0138] A lower cost solution is to have either one or both sides of
a communication link without an IrDA controller perform a simple
near-field activity flag that is functionally similar to pushing
the synchronizing buttons on both devices. If one device is
transmitting a near-field repetitive pattern, then the receiver
will output the repetitive pattern when placed in close proximity
to the transmitting near-field device. The repetitive pattern may
then be recognized as a synchronizing signal by the wireless device
that wishes to synchronize and is placed close to the transmitting
device. Either the device receiving the synchronizing signal can
send back a simple acknowledge pulse or pattern between the
requesting device's transmission of the repetitive pattern, or the
wireless link can command a change in near-field transmitting
pattern of the other device to confirm that the device that is
sending the near-field signal is the same one as the wireless link.
These patterns and responses can be generated either by an IrDA
controller driving an IrDA/Near-Field transceiver or by a simple
logic sequence, if driving only a Near-Field transceiver that is
used exclusively for synchronizing. This method of pairing is not
highly secure, since all of the pairing information is sent over
the wireless link, but it does avoid the need for a near-field
communications controller or software stack.
[0139] Integrating a USB transceiver with a near-field transceiver
compatible with an IrDA/Near-Field transceiver illustrates an
example of synergy between wired and near-field integration. A
near-field connection on USB ports would be useful, for example to
facilitate USB communication between a personal computer (PC) and a
battery powered, portable device; such as, cell phones or digital
cameras. In small portable devices, even if a USB connector is
available, it tends to be a small or non standard size that
requires a special bridge cable supplied by the camera or cell
phone vendor. These cables often get lost or misplaced creating
frustration when needed for occasional transfers. However,
convincing product manufacturers to accept any new wireless
physical layer protocol to a USB interface, no matter how low the
cost or high the performance, is virtually impossible without a
significant installed base or a rapidly growing installed base. As
indicated above, by including a near-field physical layer
transceiver in combination with an IrDA transceiver may allow the
creation of a rapidly growing installed base by replacing IrDA
transceivers on products in production or development with more
desirable IrDA/Near-Field transceivers at only a slight increase in
cost. In addition, providing an IrDA/Near-Field dongle for
interfacing to a USB plug could facilitate bridging between USB and
IrDA/Near-Field since USB to IrDA versions already exist. This
allows ready back compatibility for the existing installed base of
USB transceivers.
[0140] As an example, the largest single market for IrDA
transceivers is cell phones in Europe and Asia. Many of these
phones have integrated cameras. Users may want to transfer pictures
from these cell phone cameras to computers using USB. Although a
large installed base of IrDA cell phones exist, the bulk of these
devices have IrDA speeds of 115.2 Kbps to 1 Mbps. If computer
makers saw an installed base of 16 Mbps to 500 Mbps near-field
transceiver capable cell phones, they might be more inclined to
include USB to near-field transceiver bridges in their products. In
fact, the installed base of camera cell phones with IrDA
transceivers exceeds the installed base of digital cameras with USB
interfaces. So, it can be seen that high speed, near field file
transfer transceivers on cell phone cameras may apply pressure for
digital cameras to have compatible near-field transceivers to
provide the same functionality that may be available in camera
phones. Since virtually all digital cameras send data to PCs, this
creates a similar pressure on PC vendors to add a near-field
transceiver to a PC USB interface.
[0141] Another approach to integrating a near-field or short range
RF transceiver with USB is to incorporate the near-field antenna
around the computer peripherals, for example a computer keyboard.
This has the advantage that the dominant keyboard interface is USB
and the keyboard is often more user accessible than a USB port or
near-field port on the computer, which may be placed under or
behind a desk. If the keyboard is a wireless key board, then the
other computer peripherals that are user accessible that might
house the near-field antenna are the computer display monitor, the
USB mouse, or the USB RF head for a wireless keyboard and mouse,
webcam, or other USB Human Interface Devices (HID).
[0142] Another approach is to combine a near-field transceiver with
a wired transceiver to use an optical transceiver similar to or the
same as IrDA to provide parallel channel status, collision, and
control signaling that cannot readily be included in the main half
duplex near-field communication channel. For example, the USB
protocol does not define a method to communicate or control these
signals embedded in the main half duplex data stream; therefore, an
optical transceiver or an IrDA transceiver with a simplified
controller could provide this parallel channel.
[0143] FIGS. 15 and 16 illustrate examples of devices equipped with
a USB capability and a near field capability. In FIG. 15, a first
device 810, which may, for example, be a keyboard, includes an
interface circuit 820 that includes a wired USB transceiver 822
combined with a near field transceiver 824. Similarly, a second
device 830 includes an interface circuit 840 that also includes a
wired USB transceiver 842 combined with a near field transceiver
844. In one embodiment, near field transceiver 824 may be utilized
to transfer data from another device, where the data is then
transferred to device 830 via USB cable 802 using USB transceivers
822 and 842. This feature may be useful when device 830, which may
be a personal computer, is difficult to access, while device 810,
e.g. a keyboard, is relatively easy for a user to access.
Alternatively, a near field communication channel between near
field transceivers 824 and 844 may be utilized as a secondary
channel for transferring, for example, control messages related to
the communication between USB transceivers 822 and 842. In FIG. 16,
a first device 850 includes an interface circuit 860 that includes
an infrared USB transceiver 862 combined with a near field
transceiver 864. Similarly, a second device 870 includes an
interface circuit 880 that also includes an infrared USB
transceiver 882 combined with a near field transceiver 884. Similar
to the embodiment of FIG. 15, the embodiment of FIG. 16 may provide
a method for easier access for near field data transfer for another
device utilizing near field transceiver 864 or near field
transceiver 864 and 884 may combine to provide a secondary
communication channel between devices 850 and 870.
[0144] Use of Near-Field Transceivers in Hearing Aids and other
products compatible with cell phone or PDA near-field transceivers:
As pointed out above, hearing aid devices have a need for a
communication means that will fit inside the tiny hearing aid for
both uploading parameters and for receiving digital audio with a
cell phone. This can be readily supplied by a near-field receiver
or transceiver inside of the hearing aid that is compatible with a
near-field transceiver in a cell phone. FIG. 7 is a diagram
illustrating an example of a near-field communication link between
a cell phone device and a hearing aid device.
[0145] Even if the cell phone near-field antenna for proximity
communication is not next to the ear-piece, another auxiliary
near-field transmit antenna, whether capacitive or inductive, can
be placed around the ear piece. When the cell phone is put into
hearing aid mode, it can send the digitized receive audio directly
from the cell phone ear piece transmit antenna to the near field
receive antenna of the hearing aid, since the two devices will
typically be positioned no more than a few centimeters away from
one another. This will allow improved intelligibility of the cell
phone signal by allowing the hearing aid to directly process the
audio data without distortion or variability in signal level as the
headphone is moved around on the ear. The cell phone may send
either digital encoded audio output from its own voice decoder or
it may send the received data before going to the voice decoder so
that the hearing aid may more appropriately recover the compressed
voice audio from the far end voice coder.
[0146] A hearing aid near-field receiver, especially if it has a
capacitive antenna, can be smaller than an IrDA transceiver and be
a simpler design that omits AGC, since the ear canal and cell phone
are fairly well shielded against near-field noise. Typically, it
does not need data rates beyond 115.2 Kbps. Consequently, the
hearing aid receiver's current consumption may be below 50 uA and,
if only powered up at a low duty cycle, may consume even less,
which will extend battery life.
[0147] Another application of the near-field receiver in a hearing
aid is that it can be used to up-load digital filter and gain
coefficients without a connector or contacts. A PDA or cell phone
could be used as the upload source and can be used as a user
friendly display terminal for programming the hearing aid. For this
function, the hearing aid may require a bi-directional near-field
transceiver so that the cell phone as a programming terminal can
read the parameters in the hearing aid. The presence of a
near-field transceiver can give the user more options to control
the hearing aid, e.g. selecting a preprogrammed mode of operation
(sleep, concert, meeting . . . ).
[0148] The same approach may be taken in order to use a PDA and
cell phone with a near-field transceiver as a convenient small
terminal to program or send data to other terminal-less devices;
such as smart light switches. If device is particularly small, then
a near field receiver on the device may be less costly than an IrDA
receiver. For many smart electronic devices, the terminal aspect of
display and keyboard are left off the product in order to reduce
cost or because there is no room for these components on the smart
device. Since virtually all PDAs have IrDA transceivers, it is
logical and desirable that PDAs acquire IrDA/Near-Field
transceivers since the near-field transceiver could be used as a
user interface to communicate with the smart devices.
[0149] FIG. 12 is a functional block diagram illustrating an
embodiment of a transceiver 720 configured to operate in infrared
and near-field modes. Mode control, in this example, is
accomplished by setting the TX input and clocking the SD line to
latch the mode setting of the TX input to buffer 732 into a
flip-flop 734, which controls a multiplexor 742 that switches
between an infrared portion of the transceiver 730 and a near-field
portion 740. Once the near-field mode is set, data received by the
near-field portion 740 of transceiver 720 will be output through
buffer 744 to a receiver output pin of the circuit 720. Once the
mode is reset, data received by the infrared transceiver 720 will
appear on the receiver output pin. FIG. 13 is a functional block
diagram illustrating an example of the transceiver of FIG. 12
operating with a controller 752 that switches the transceiver 720
between infrared and near-field modes and interfaces with a
microprocessor 760. The controller 752 determines the mode of
operation of the transceiver 720 and relays data to and from the
microprocessor 760.
[0150] FIG. 14 is a functional block diagram illustrating an
example of a capacitive receiver circuit for use in receiving
signals in a capacitive near-field transceiver device. A hysteresis
comparator 770 compares the signal received from a capacitively
coupled receiver input to pin RXCAP to an analog ground level input
to pin GNDCAP in order to generate and output a received near-field
data signal. FIG. 14 is a functional block diagram illustrating an
example of a capacitive transmitter circuit for use in transmitting
signals in a capacitive near-field transceiver device. A digital
driver 790 outputs a transmit data signal to a capacitive transmit
coupling to pin TXCAP in order to send a near-field data
signal.
[0151] In one embodiment, a half-duplex near-field transceiver is
combined with an IrDA module on the same integrated circuit die,
where the TX and RX signals are substantially compatible with IrDA
module TX and RX signals. This embodiment may be further refined by
using the IrDA module shield as an antenna for the near-field
transceiver, as illustrated in FIG. 1.
[0152] In another embodiment, an IrDA transceiver is combined with
a Near-field transceiver having a single ended capacitive
near-field antenna. The antenna can be implemented, for example, as
an existing metal shield around the IrDA module, a single metal
plate in front of the module, or as a conductive trace on a printed
circuit board (PCB), which is connected to an interface pin on the
transceiver module. FIG. 2 illustrates the use of an inductive
auxiliary transmit loop antenna with a combined IrDA and near-field
transceiver. In a further embodiment, the receiving antenna for the
near-field device is the IrDA shield, but a separate auxiliary
antenna is used for transmitting, as shown in FIGS. 2 and 3. For
higher proximity security, a smaller transmitting antenna may be
used. In addition, the phasing of IrDA shield and TX input may be
designed to be the same, so that the TX data input of the
transceiver can drive the larger auxiliary TX antenna. In a further
embodiment, the connection to the shield is via a contact or small
capacitor between the IrDA/near-field transceiver circuit package
formed between shield and trace areas on the module.
[0153] In one embodiment, an IrDA transceiver is combined with a
Near-field transceiver having a single ended inductive near-field
antenna (FIG. 2). The IrDA/Near-field inductive near-field antenna
can be implemented as an existing metal shield around IrDA module,
a conductive loop on the PCB or a conductive wire around the
transceiver module or on a packaging case. In a further embodiment,
the combined IrDA/Near-Field transceiver uses the IrDA shield as
the near field antenna with another shield 124 behind the IrDA
shield to reduce local near field noise.
[0154] In still another embodiment, a half-duplex near-field
transceiver is provided where the transmitting antenna generates
both an inductive and capacitive near-field by putting the current
limiting resistor at the end of the transmit antenna loop 122 and
the receiver is configured to determine which receiving mode is
best and utilize the best mode. In a further embodiment, the half
duplex baseband near-field transceiver is bridged to a USB or
Firewire (IEEE 1394) system.
[0155] In yet another embodiment, an infrared transceiver provides
a parallel channel for other USB status and control signals.
Another embodiment incorporates a half duplex near field
transceiver antenna around the edges of USB driven computer
peripherals, such as keyboards, display monitors, wireless keyboard
and mouse drivers.
[0156] One embodiment involves a baseband near field system with
AGC and automatic time out that reverts a hysteresis receiver back
to idle state after a pre-determined amount of time. Another
embodiment provides for controlling the detect bandwidth responsive
to the automatic gain control (AGC) level exceeding a threshold, so
that the data rate is adjusted for signal level. Another embodiment
provides for an adjustable AGC bandwidth threshold.
[0157] In another embodiment, a half duplex near field receiver
with a capacitive antenna is configured such that the AGC bandwidth
threshold is adjustable with a resistor 228, 248 tied to the
antenna input, as shown in FIG. 3. In a further embodiment, a half
duplex near field receiver is configured such that a detect
threshold is adjustable by using a resistor 249 in series with the
shutdown (SD) control pin. In another embodiment, a resistor 249
connected to an antenna pin is used to adjust minimum detect
threshold. In these embodiments, a resistor is connected to a
digital input/output pin so that the I/O pin is multiplexed for use
as an antenna or digital signal interface during normal operation
and to set an operating parameter of the transceiver circuit, such
as during an initialization cycle. During initialization, for
example, a voltage is output from the circuit onto the I/O pin and
the resulting current flow is measured by the circuit in order to
determine the magnitude of the resistance. The operating parameter
is then set based on the magnitude of the measured current. Once
the parameter is set, the voltage is removed from the I/O pin,
which returns to functioning as a digital signal interface or
antenna interface. In another embodiment, digital serial shift
loading of adjustments to operating parameters is performed.
[0158] In another embodiment, a near-field baseband receiver
includes an AGC circuit with fast attack that introduces an
anti-signal when AGC gain decreases in response to an input signal.
The anti-signal is larger than the worst case integrated circuit
(IC) mismatch.
[0159] In an embodiment, a near-field receiver is combined with an
IrDA transceiver that can operate in either baseband or carrier
mode.
[0160] In an embodiment, a half duplex baseband near-field
transceiver is combined with a IEEE 802.11 or Bluetooth transceiver
in order to synchronize and securely pass encryption keys, as
illustrated in FIGS. 6 and 7.
[0161] In an embodiment, a controller for a half duplex near-field
inductive baseband transceiver is configured for phase inversion
detection by correlating preamble syncs with in phase or out of
phase syncs.
[0162] In an embodiment, an IrDA/Near-Field device is combined in
an electronic device, such as a cell phone, for communication with
a compatible baseband Near-Field transceiver in another electronic
device, such as a headphone, in order to synchronize communication
between wireless transceivers, such as Bluetooth, in both devices.
See FIGS. 6 and 7. In a further embodiment, proximity pairing
wireless transceivers (Bluetooth, WiFi) are provided with a simple
repetitive baseband near-field signal.
[0163] Another embodiment provides for using a cell phone
near-field transmitting antenna around the cell phone ear piece to
send audio digital data from either before voice decoder or after
it to be sent directly to a near-field receiver in a hearing aid. A
further embodiment provides for sending digital audio to the
hearing aid from any device by using a near-field transceiver, such
as PDA, cell phone, headphones.
[0164] An additional embodiment provides for using a cell phone,
PDA or other device equipped with a near-field transceiver to
upload control parameters to a hearing aid or to any other terminal
less electronic device. A further embodiment provides for control
of the operation of a hearing aid or any other portable
terminal-less electronic device by means of another near-field
device such as cell phone, PDA, etc.
[0165] All references, including publications, patent applications,
and patents, cited herein are hereby incorporated by reference to
the same extent as if each reference were individually and
specifically indicated to be incorporated by reference and were set
forth in its entirety herein.
[0166] The use of the terms "a" and "an" and "the" and similar
referents in the context of describing the invention (especially in
the context of the following claims) are to be construed to cover
both the singular and the plural, unless otherwise indicated herein
or clearly contradicted by context. Recitation of ranges of values
herein are merely intended to serve as a shorthand method of
referring individually to each separate value falling within the
range, unless otherwise indicated herein, and each separate value
is incorporated into the specification as if it were individually
recited herein. All methods described herein can be performed in
any suitable order unless otherwise indicated herein or otherwise
clearly contradicted by context. The use of any and all examples,
or exemplary language (e.g., "such as") provided herein, is
intended merely to better illuminate the invention and does not
pose a limitation on the scope of the invention unless otherwise
claimed. No language in the specification should be construed as
indicating any non-claimed element as essential to the practice of
the invention.
[0167] Preferred embodiments of this invention are described
herein, including the best mode known to the inventors for carrying
out the invention. It should be understood that the illustrated
embodiments are exemplary only, and should not be taken as limiting
the scope of the invention.
* * * * *
References